1. Field of the Invention
The present invention relates to head up display (HUD) systems and more particularly to a meniscus combiner for a HUD.
2. Description of the Related Art
A Head Up Display (HUD) is a means of projecting information directly into a human's visual field. The HUD was pioneered for military aviation and has since been used in other applications. HUDs are typically used in aircraft to provide pilots with information superimposed onto their forward field of view through the aircraft windshield. The information displayed may be data or symbolic images indicative of flight conditions such as the operating condition of the aircraft, environmental information or guidance information for use in directing the aircraft to its destination. These images are presented in overlying fashion on the pilot's field of view so as not to interfere with the pilot's view of the background scene.
The combiner of the HUD is s critical component to provide a collimated display image to an operator for a given Field of View (FOV) at a given design reference point. The HUD combiner components are generally large in size. The current HUD combiners are typically comprised of two optical components and with reflection holograms or dielectric coatings on some of the surfaces. They are cemented together or co-mounted in the HUD system configuration which induces complicated assembly and high cost of the HUD system.
Often, HUD applications include the use of combiners with doublet lens. The doublet combiner is composed of a convex front lens and a concave back lens. The convex surface of the convex lens is dichroic or holograhphically coated for reflecting the HUD format information. Since the optical power of the front lens cancels the optical power of the back lens, there is no optical effect when viewing through the combiner.
U.S. Pat. No. 5,907,416, entitled “Wide FOV Simulator Heads-Up Display With Selective Holographic Reflector Combined”, issued to M. Cheren et al, discloses a wide field-of-view simulator heads-up display that provides images to a user along an optical axis. A HUD CRT provides images of a predetermined design wavelength, while rear projection screen CRTs provide out-of-window scenery that does not contain the predetermined design wavelength. A curved holographic combiner is mounted on the optical axis with a reflective hologram on a concave surface covered with a urethane overcoat. The convex surface has an antireflective coating. A tilted beamsplitter cooperates with a folding mirror in a relay optical system for providing a virtual image of the HUD CRT for reflection from the holographic combiner.
U.S. Pat. No. 4,968,117, entitled “Graded Index Aspheric Combiners and Display System Utilizing Same”, issued to Chern et al, discloses an optical combiner that includes a substrate with at least one aspheric surface and a diffraction-type reflective coating formed on the substrate for selectively reflecting radiation within one or more predetermined narrow band ranges of wavelengths impinging on the coating. The asphericity of the surface may be selected to compensate or balance optical aberrations. The coating is advantageously a graded-index coating, which eliminates the possible degradation of gelatin hologram coatings due to moisture. A process for applying the graded-index coating to a substrate is disclosed. The variation in the index profile of the coating can be selected to provide the capability of combiners with multiple color reflectivity responses, or which allow use of display light sources of wider spectral bandwidth, resulting in a brighter image and improved angular bandwidth. In another disclosed embodiment, the combiner is incorporated in a biocular helmet visor display resulting in improved optical performance and a simpler, lightweight structure. In another embodiment, the combiner is incorporated into a head-up display for an aircraft resulting in improved performance, lower weight, improved safety and greater look-up capability.
U.S. Pat. No. 6,088,165, entitled “Enhanced Night Vision Device”, issued to D. J. Janeczko et al, discloses night vision device comprising a facemask housing assembly having a peripheral surface defined by a rear surface contoured to a user's face and an open front surface, the housing assembly operative for encasing a pair of optical assemblies operative for receiving light from a viewed object via a first folded optical path and via a second direct optical path, combining the light from the first and second paths, and directing the combined light to a user's eye for viewing the object; where each optical assembly detachably coupled to the housing assembly. Each optical assembly comprises an objective lens assembly for receiving and focusing visible and infrared light from a viewed object along the first folded optical path; image intensifier means responsive to the focused light from the objective lens assembly for converting the visible and infrared light to visible intensified light; and beam combining means responsive to the visible intensified light and to the direct path light from combining with one another and directing the combination to the user's eye for viewing.